Field
Exemplary embodiments of the present disclosure relate to a lighting apparatus using a dimmable alternating current-driven light emitting diode (LED), and more particularly, to an alternating current (AC)-driven LED lighting apparatus which allows dimming control through phase cut control and exhibits idealistic and stable variation of a dimming level over an entire interval of the dimming level using a triode for alternating current (TRIAC) dimmer. In addition, exemplary embodiments of the present disclosure relate to an AC-driven LED lighting apparatus which can improve compatibility of the TRIAC dimmer.
Discussion of the Background
Generally, a light emitting diode (LED) can be driven only by direct current (DC) power due to inherent characteristics thereof. Thus, a lighting apparatus employing such a conventional LED is limited in applicability and requires a separate circuit such as a switching mode power supply (SMPS) when used in domestic settings employing AC 220V power. As a result, the lighting apparatus has problems such as complicated circuit design and high manufacturing costs.
In order to solve such problems, various studies have focused on development of an AC-driven LED lighting apparatus which includes a plurality of light emitting cells connected to each other in series or in parallel and can be driven by AC power.
In order to solve the above problems in the related art, sequential driving of AC-driven LEDs has been suggested. In this sequential driving method, assuming that a lighting apparatus includes three groups of LEDs, under conditions that an input voltage increases over time, a first LED group starts to emit light in a first stage driving interval; a second LED group is connected in series to the first LED group and the first and second LED groups are turned on to emit light in a second stage driving interval in which a drive voltage is higher than the drive voltage in the first stage driving interval; and first to third LED groups are turned on to emit light in a third stage driving interval in which the drive voltage is higher than the drive voltage in the second stage driving interval. In addition, under conditions that the drive voltage decreases over time, first, the third LED group stops light emission in the second stage driving interval, the second LED group stops light emission in the first stage driving interval, and the first LED group finally stops light emission at a drive voltage lower than the drive voltage of the first stage driving interval such that an LED drive voltage approaches the input voltage.
On the other hand, LED dimming control refers to an operation of changing luminescent flux or illuminance (Lux) of an LED lighting apparatus, that is, brightness of a light source, according to voltage applied thereto, and a dimmable light source means a system configured to perform such illuminance control in the lighting apparatus. Such a dimmable system is provided to the LED lighting apparatus in order to reduce power consumption and enables efficient operation of the LED lighting apparatus. Particularly, heat generated during continuous light emission from LEDs causes deterioration in quality and efficiency of a lighting operation. Accordingly, in order to satisfy user demand while reducing power consumption, a dimming function is generally provided to the LED lighting apparatus. Among such LED lighting apparatuses having the dimming function, since a DC-driven LED lighting apparatus is driven by converting AC power into DC power through an SMPS, the DC-driven LED lighting apparatus allows relatively easy dimming and thus can be expected to have a certain degree of dimming control characteristics. However, since a typical AC-driven LED lighting apparatus as described above drives LEDs using only a rectified voltage obtained through rectification of AC voltage, the AC-driven LED lighting apparatus has difficulty realizing the dimming function and securing linearity in dimming control. Particularly, a sequential driving type AC-driven LED lighting apparatus has a problem in that drive voltage becomes unstable due to temporary increase or decrease in drive voltage by internal impedance of an AC power supply line and a dimmer as soon as LEDs are tuned on or turned off for the next operation when the number of LED groups turned on to emit light is changed depending upon the magnitude of the drive voltage (for example, upon change from fourth stage driving to third stage driving, upon change from third stage driving to second stage driving, and the like). That is, a typical AC-driven LED lighting apparatus having the dimming function suffers from irregular variation of luminescent flux in some dimming control intervals instead of enabling variation in the luminescent flux over an entire interval of the dimming level.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the inventive concepts, and, therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.